Acoustical damping is a significant concern for certain structural components of aerospace vehicles including aircraft and spacecraft. In particular, acoustical damping is often required to protect instrumentation from damage due to the noise generated by vehicle thrust/propulsion systems. For example, acoustical damping is generally used to protect spacecraft payloads from the noise generated by launch vehicle thrusters and, in certain cases, is desirable to protect aircraft instrumentation from noise generated by aircraft engines. In some cases, it has been estimated that instruments inside an unprotected payload fairing would experience in excess of 150 dB due to the launch vehicle thrusters if left unprotected. Such noise levels can damage or incapacitate sensitive payload instruments, resulting in aborted missions, suboptimal spacecraft performance and substantial scientific or commercial losses. In order to provide the desired acoustical damping, aerospace vehicles are often equipped with acoustical add-ons or liners. Such liners include passive damping systems such as fiber glass or other insulating liners and active damping systems such as any of various dynamic sound attenuating systems. In either case, such systems are typically attached to an inside surface of the vehicle structure so as to provide a lining around the volume to be protected.
These liners generally impose certain limitations on mission design. In some cases, such liners provide inadequate damping or damping that is poorly matched to a potentially damaging frequency, frequency range, or ranges. In addition, such liners often involve substantial extra mass thereby limiting payload potential. In all cases, the use of a liner inside the vehicle structure reduces the vehicle volume that is available for instrumentation or other payload systems.
Active Helmholz resonators have been proposed for certain aerospace vehicle applications. However, these have generally been proposed as liners or other add-ons with attendant weight/volume limitations, have not provided adequate or selective damping and/or have not addressed lightweight composite construction such as SNAPSAT applications.